title: Luminescent P-chirogenic copper clusters.
abstract: P-chirogenic clusters of the cubanes [Cu4I4L4] (L = chiral phosphine) were prepared from (+)- and (-)-ephedrine with L = (S)- or (R)-(R)(Ph)(i-Pr)P (with R = CH3 (seven steps) or C17H35 (10 steps)) with e.e. up to 96%. The X-ray structure of [Cu4I4((R)-(CH3)(Ph)(i-Pr)P)4] confirmed the cubane structure with average Cu···Cu and Cu···I distances of 2.954 and 2.696 Å, respectively. The cubane structure of the corresponding [Cu4I4((S)-(CH3)(Ph)(i-Pr)P)4] was established by the comparison of the X-ray powder diffraction patterns, and the opposite optical activity of the (S)- and (R)-ligand-containing clusters was confirmed by circular dichroism spectroscopy. Small-angle X-ray scattering patterns of one cluster bearing a C17H35 chain exhibit a weak signal at 2θ ~ 2.8° (d ~ 31.6 Å), indicating some molecular ordering in the liquid state. The emission spectra exhibit two emission bands, both associated with triplet excited states. These two bands are assigned as follows: the high energy emission is due to a halide-to-ligand charge transfer, XLCT, state mixed with LXCT (ligand-to-halide-charge-transfer). The low energy band is assigned to a cluster-centered excited state. Both emissions are found to be thermochromic with the relative intensity changing between 77 and 298 K for the clusters in methylcyclohexane solution. Several differences are observed in the photophysical parameters, emission quantum yields and lifetimes for R = CH3 and C17H35. The measurements of the polarization along the emission indicate that the emission is depolarized, consistent with an approximate tetrahedral geometry of the chromophores.
authors.affiliation: Département de Chimie, Université de Sherbrooke, 2500 Boul. Université, Sherbrooke, Québec, Canada J1K 2R1.
authors.forename: Antony
authors.initials: A
authors.lastname: Lapprand
authors.forename: Mathieu
authors.initials: M
authors.lastname: Dutartre
authors.forename: Naïma
authors.initials: N
authors.lastname: Khiri
authors.forename: Etienne
authors.initials: E
authors.lastname: Levert
authors.forename: Daniel
authors.initials: D
authors.lastname: Fortin
authors.forename: Yoann
authors.initials: Y
authors.lastname: Rousselin
authors.forename: Armand
authors.initials: A
authors.lastname: Soldera
authors.forename: Sylvain
authors.initials: S
authors.lastname: Jugé
authors.forename: Pierre D
authors.initials: PD
authors.lastname: Harvey